Process for oil recovery using mixed surfactant composition

ABSTRACT

A process for the recovery of oil from subterranean reservoirs by injecting an aqueous fluid containing from about 0.05 to about 2.0% by weight of a bi-functional surfactant or a mixture of surfactants containing one or more of the following structures; 
     
       
         
         
             
             
         
       
     
     Optionally the aqueous fluid may contain mixtures of individual surfactants having carboxylic, and sulfonate or sulfate functionalities. The remainder of the composition includes water or brine, a cosolvent and optionally a viscosity control agent, and optionally an alkali.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on provisional application Ser. No. 60/773,398filed on Feb. 16, 2006.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

DESCRIPTION OF ATTACHED APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates to a process for the recovery of oil fromsubterranean oil bearing reservoirs, and more particularly the presentinvention is to improved oil recovery operations involving the injectioninto reservoirs of a composition containing mixtures of surfactantscontaining a weak anionic functionality group and a strong anionicfunctionality group.

In the recovery of oil from subterranean reservoirs it usually ispossible to recover approximately 15%-20% of the original oil in placeby primary recovery. Secondary recovery methods such as well stimulationor water flooding are applied after the amount of oil recovered byprimary recovery becomes uneconomical. Secondary recovery methods canrecover approximately an additional 15%-30% of the original oil in placewhich leaves the reminder of the oil unrecoverable unless other meanssuch as tertiary recovery processes are applied. These tertiary recoverymethods include but are not limited to the use of miscible andimmiscible gases and liquids, steam, foam, alkali, surfactants, andpolymers.

It has been known that many factors including but not limited to theinterfacial tension between the injection brine and the residual oil,the relative mobility of the injected brine, and the wettabilitycharacteristics of the rock surfaces comprising the reservoir are allimportant in determining the amount of oil recovered by tertiaryrecovery. Numerous studies have found that the addition of surfactantsto the injection brine can alter the interfacial and wetting propertiesto help overcome the high capillary pressure and increase the oilrecovery. In many cases the addition of a polymer along with thesurfactant or immediately after the surfactant can increase the mobilityratio between the injected brine and oil thus further improving thesweep efficiency of the flood.

Because the injection brine composition varies, it is important to usethe brine available at the injection site for the tertiary process inorder to be economically feasible. It is important to have surfactantsthat are compatible with brines having wide ranges of total dissolvedsolids (TDS) and divalent cations such as those of calcium andmagnesium. The problem with many of the presently used surfactants intertiary oil recovery is that they are incompatible with the brinescontaining high TDS and divalent cations that are often found at theinjection site. Costly water treatment processes or using an alternatefresh water source makes the tertiary recovery process economicallyunfeasible in many cases. Therefore it is important to have surfactantsthat are tolerant to the high TDS and divalent cations.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to the composition of surfactantscontaining a weak anionic functionality group and a strong anionicfunctionality group, which composition is formulated into a concentratedsurfactant blend containing a aqueous solvent such as water or brine,and a co-surfactant/solvent such as a lower molecular weight alcohol oralcohol ether. The concentrated surfactant blend is added in aconcentration range of about 0.05% to about 5% to the injection brineand introduced into the subterranean hydrocarbon containing formation by(a) injecting into said formation through one or more injection wells,and (b) displacing said solution into the formation to recoverhydrocarbons from one or more production wells. The injection andproducing wells may be the same or different. Depending on the reservoirconditions, other additives may be added to the injection brineincluding strong or weak alkalis, viscosifiers, corrosion and scaleinhibitors, and others known to those familiar with the art.

In the present invention, the weak and strong anionic functionalitygroups may be combined into the same molecule as a bi-functionalsurfactant, or be present as mixtures of surfactants containing one ormore strong anionic functionality group and one or more weak anionicfunctionality group.

Non-exclusive examples where the weak and strong functionality groupsare included in the same molecule as bi-functional surfactant are:

where m+n=5-28

M=H, Na, K, NH₃, Amine, Ca, Mg, Y=H, CH₃, or CH₃CH₂,

and x=0-30 or more

The product described in Structure I is made by sulfonating anunsaturated fatty acid using any of a number of sulfonation processesknown to those familiar with the art including, but not limited to, SO₃thin film sulfonation, oleum, chlorosulfonic acid, cold SO₂/SO₃ andsulfamic acid. The product described in Structure II is made by reactingthe carboxylated phenol with sulfonic acid obtained from the sulfonationof an olefin using the procedure described in U.S. Pat. No. 6,043,391.The phenol moiety may contain from about 0 to about 30 or more moles ofan alkoxy group such as ethylene oxide (EO), propylene oxide (PO), ormixtures of EO and PO, or sequences of EO and PO, to adjust thesolubility and molecular weight of the surfactant.

Non-exclusive examples of the mixtures of surfactants containing one ormore strong anionic functionality group and one or more weak anionicfunctionality group are: linear alkoxylated alcohol carboxylates,branched alkoxylated alcohol carboxylates, carboxylated arylalkoxylates, linear alkyl aryl sulfonates, branched alkyl arylsulfonates, aryl linear alkyl sulfonates, aryl branched alkylsulfonates, linear alkyl ether sulfates, branched alkyl ether sulfates,linear alkyl ether sulfonates, branched alkyl ether sulfonates, linearalkyl sulfates, branched alkyl sulfates, linear alkyl sulfonates,branched alkyl sulfonates, and their salts including, Na, K, NH₃, Amine,Ca, Mg.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed descriptions of the preferred embodiment are provided herein.It is to be understood, however, that the present invention may beembodied in various forms. Therefore, specific details disclosed hereinare not to be interpreted as limiting, but rather as a basis for theclaims and as a representative basis for teaching one skilled in the artto employ the present invention in virtually any appropriately detailedsystem, structure or manner.

The present invention is directed to the composition of salt anddivalent cations tolerant surfactants containing a weak anionicfunctionality group and a strong anionic functionality group forrecovering crude oil from subterranean hydrocarbon formation. The weakand strong anionic functionality groups may be combined into the samemolecule as one or more bi-functional surfactants or mixtures ofsurfactants containing one or more strong anionic functionality groupand one or more weak anionic functionality group may be used.

Non-exclusive examples of the weak and strong functionality groups areincluded in the same molecule as bi-functional surfactants are:

where m+n=5-28

M=H, Na, K, NH₃, Amine, Ca, Mg, Y=H, CH₃, or CH₃CH₂,

and x=0-30 or moreThe product described in Structure I is made by sulfonating anunsaturated fatty acid using any of a number of sulfonation processesknown to those familiar with the art including but not limited to SO₃thin film sulfonation, oleum, chlorosulfonic acid, cold SO₂/SO₃ andsulfamic acid. The product described in Structure II is made by reactinga carboxylated phenol with the sulfonic acid obtained from thesulfonation of an olefin as described in U.S. Pat. No. 6,043,391. Thephenol moiety may contain from about 6 to about 30 or more moles of analkoxy group such as EO PO, or mixtures of EO and PO, or sequences of EOand PO, to adjust the solubility and molecular weight of the surfactant.

Non-exclusive examples of the mixtures of surfactants containing one ormore weak anionic functionality groups and one or more strong anionicfunctionality groups are mixtures of linear alkoxylated alcoholcarboxylates, branched alkoxylated alcohol carboxylates, carboxylatedarylalkoxylates, with linear alkyl aryl sulfonates, branched alkyl arylsulfonates, aryl linear alkyl sulfonates, aryl branched alkylsulfonates, linear alkyl ether sulfates, branched alkyl ether sulfates,linear alkyl ether sulfonates, branched alkyl ether sulfonates, linearalkyl sulfates, branched alkyl sulfates, linear alkyl sulfonates,branched alkyl sulfonates, and their salts including, Na, K, NH₃, Amine,Ca, Mg.

Specific, but not limiting examples, are mixtures of sodium C1416alpha-olefin sulfonate (AOS) with branched sodium tridecyl-6 EOcarboxylate. Another example is a blend of linear sodium alkyl benzenesulfonate, branched sodium alkyl benzene sulfonate and sodiumnonylphenol-10 EO carboxylate.

The ratio of the weak to strong anionic functionality groups isdetermined by the characteristics of the crude oil, the brine,temperature and the type of formation in which they are to be used. Thefinal composition is formulated so that it is compatible with the brineand enhances the recovery of oil under the bottom hole conditions.

The present invention of a process using surfactants containing a weakanionic functionality group and a strong anionic functionality group areusually formulated into a concentrated surfactant blend containing aaqueous solvent such as water or brine, and a co-surfactant/solvent suchas a lower molecular weight alcohol or alcohol ether. Non-exclusiveexamples of the co-surfactant/solvent are iso-propanol, n-butanol, andethylene glycol monobutyl ether. The concentrated surfactant solution isadded in a concentration range of about 0.05% to about 5% to the brineand introduced into the subterranean hydrocarbon containing formation by(a) injecting into said formation through one or more injection wells,and (b) displacing said solution into the formation to recoverhydrocarbons from one or more production wells. The injection andproducing wells may be the same or different. Depending on the reservoirconditions, other additives may be added to the injection brineincluding strong or weak alkalis, viscosifiers, corrosion and scaleinhibitors, and others known to those familiar with the art.

The concentrated surfactant blend containing strong and weak anionicfunctionality groups are compatible and can be added to a wide range ofbrines containing different amount of total dissolved solids andmultivalent cations such as Ca⁺² and Mg⁺² and injected into the oilbearing reservoirs to recover residual oil. They can also be injectedwith gas, such as N₂ or CO₂.

In accordance with a preferred embodiment of the invention, there isdisclosed a process for improving the recovery of oil by injecting intoone or more injection wells a fluid containing

-   -   a) one or more bi-functional surfactants containing both a weak        and a strong anionic functionality groups on one molecule, or a        mixture of a least one or more surfactant containing a strong        anionic functionality group and at least one or more surfactants        containing a weak anionic functionality group,    -   b) an aqueous based solvent,    -   c) optionally one or more co-surfactants/solvents,    -   d) optionally a viscosity improving agent, and    -   e) optionally an alkali,    -   and recovering the oil from one or more of the same or different        producing wells.

The preferred strong anionic functionality is derived from a sulfate orsulfonate group and the preferred weak anionic functionality is derivedfrom a carboxylate group. The aqueous solvent may be water or asynthetic brine or a brine that is produced from the reservoircontaining various mono and divalent ion salts including but not limitedto the sulfonate, chloride, carbonate and/or bicarbonate salts ofsodium, potassium, calcium, magnesium, strontium, barium, and/or ironoriginally present or intentionally added to the aqueous solvent. Theco-surfactant/solvent includes but is not limited to a short chainedalcohol, glycol, or ether such as methanol, ethanol, propanol,Isopropanol, butanol, iso-butanol, glycerin, ethylene glycol, propyleneglycol, ethylene glycol monobutyl ether. The alkali includes but is notlimited to sodium hydroxide or sodium carbonate. The viscosity improvingagent may includes but is not limited to any of a number of polymersknown to those familiar with the art including polyacrylamide, xanthangum, and block polymers of acrylamide and Copolymer of acrylic acid and2-Acrylamido-2-Methylpropyl Sulfonic Acid.

An objective of the present invention is to provide a process for therecovery of oil from subterranean reservoirs using surfactantcomposition to improved oil recovery that is effective over a wide rangeof electrolyte and divalent anion concentrations.

Another objective of the present invention is to provide a process forthe recovery of oil from subterranean reservoirs using a surfactantcomposition to improved oil recovery with minimum adsorption onto theformation.

Other objectives and advantages of the present invention will becomeapparent from the following descriptions, taken in connection with theaccompanying drawings, wherein, by way of illustration and example, anembodiment of the present invention is disclosed.

Following are examples illustrating the utility of the present inventionfor application in the recovery of oil from subterranean reservoirs. TheInterfacial tension (IFT) between the crude oil/injection brine usingthe composition of the present invention is used to illustrate theefficiency of the present invention. It is well documented that afterprimary oil recovery and secondary oil recovery the Capillary Number isabout 10⁻⁶. See for instance Basic Concepts in Enhanced Oil RecoverProcesses, p 18-19, 90. The capillary number is defined as:

Nc=μV/σ

where

Nc=Capillary Number

μ=displacing fluid viscosityV=interstitial velocityσ=IFT between the displacing fluid and the crude oil.

Increasing the Capillary Number to a value above 10⁻³ has been shown toresult in a substantial increase in the recovery of trapped oil afterwaterflooding has become ineffective (Basic Concepts in Enhanced OilRecover Processes, p 108). The viscosity and the velocity cannot beincreased substantially without damaging the reservoir, however, the IFTcan easily be reduced 3 to 4 orders of magnitude by the proper choice ofsurfactant. Thus a surfactant can reduce the IFT between an oil and anaqueous medium from 3-30 mN/m to less than 10⁻² mN/m resulting in anincrease in the capillary number to greater than 10⁻² and improve theoil recovery.

In the following examples, IFT has been used as a measure of thesuitability of a particular surfactant as a candidate for enhanced oilrecovery.

Table I lists the surfactants used to in the examples chosen todemonstrate the utility and novelty of the invention. In all cases thesurfactant formulation consisted of 50% by weight surfactant, 25% byweight Ethylene glycol Monobutyl ether (co-surfactant/solvent), and 25%by weight water. Also in all cases the surfactant formulation was addedto the injection brine at a concentration of 0.10 weight percent.

TABLE I Surfactants Used In Examples SURFACTANT CHEMICAL DESCRIPTIONFUNCTIONALITY DESCRIPTION A Sodium salt of linear dodecyl benzeneSurfactant with strong anionic sulfonate EW = 342 functionality group BSodium salt of linear dodecyl benzene Surfactant with strong anionicsulfonate EW = 405 functionality group C Sodium salt of nonylphenol + 10EO Surfactant with weak anionic carboxylate functionality group D Sodiumsalt of sulfonated erucic acid Surfactant with both weak and strong(structure I where M = Na, m + n = 19) anionic functionality groups ESodium salt of sulfonated oleic acid (structure Surfactant with bothweak and strong I where M = Na, m + n = 15) anionic functionality groupsF Sodium salt of alkoxylated alkylphenol Surfactant with both weak andstrong sulfonate (structure II where M = Na, m + n = 12, anionicfunctionality groups and x = 10)

Table II is the brine compositions that were used for the IFT testing toshow the effect of total dissolved solids and divalent ion concentrationon the IFT obtained using various surfactants.

TABLE II Brine Compositions BRINE 1 2 3 NaCl, % 1.0 7.0 10.0 CaCl2—2H2O,% 0.1 0.1 1.5 MgCl2—6H2O, % 0.1 0.1 1.5

Table III compares the IFT obtained with 0.10% by weight of varioussurfactant concentrates in the three brines against a crude oil having34 API Gravity at 42° C. All IFTs were obtained using a University ofTexas Model 500 spinning drop interfacial tensiometer after spinning at42° C. for 1 hour.

TABLE III Comparison of IFTs With Various Surfactants Oil API Gravity =34 Testing Temperature = 42° C. TEST SURFACTANTS BRINE 1 BRINE 2 BRINE 31 A 0.225 Precipitate Precipitate 2 B 0.177 Precipitate Precipitate 3 C0.077 0.092 0.191 4 D 0.0097 0.0072 0.0075 5 E 0.0086 0.0012 0.0016 61:1 A + C 0.0029 0.0057 0 0.0076 7 1:1 B + C 0.0054 0.0063 0.00089 81:1:1A + B + C 0.0087 0.0021 0.0023 9 1:1 D + E 0.0045 0.0051 0.0051 10F 0.0022 0.0023 0.00298

The data obtained from Table III shows that surfactant A and B aresoluble in the lower salt concentration Brine 1, yet the IFTs are toohigh to effectively remove the residual oil. Furthermore, surfactants Aand B are not salt tolerant and precipitated in Brines 2 and 3.Surfactant C is salt tolerant in all 3 brines, however, it did notprovide low IFT required for oil recovery. Surfactants E, F and themixture of surfactants as described in Test numbers 7-10 are salttolerant and also provides low IFT necessary for oil recovery. The datain Table III demonstrated the unexpected low IFT and brine tolerance byusing surfactants containing a weak anionic functionality group and astrong anionic functionality.

The ratio of the surfactant with strong anionic functionality group andthe surfactant with weak anionic functionality group can be furtheroptimized by varying their ratio based on the crude oil and brineproperties as demonstrated in Table IV.

TABLE IV Effect of IFT On Various Ratios of Surfactants D and E in BRINE3 Crude Oil API Gravity = 27 Temperature = 65° C. Surfactant D, %Surfactant E, % IFT, mN/m 100 0 0.891 75 25 0.0080 50 50 0.0058 25 750.0023 0 100 0.356

Table IV shows that surfactants D and E did not work effectively bythemselves. By mixing surfactant D and E at various ratios, the optimumratios for the crude oil and brine tested was 25% surfactant D and 75%surfactant E.

Based on the results revealed above in Tests 1-10 a process has beendeveloped where a composition for the recovery of oil from subterraneanreservoirs is injected into one or more injection wells comprised of

a) one or more bi-functional surfactants having both sulfonate andcarboxylate functionality,

b) one or more co-surfactants/solvents

c) optionally a viscosity control agent

d) optionally an alkali, and

e) an aqueous based solvent

The one or more bi-functional surfactants having both sulfonate andcarboxylate functionally have the following formula:

Where m+n is 5 to 28, preferably 9 to 21 and most preferably 15 to 19,X is 0 to 30, preferably 0 to 15, and most preferably 4 to 12,

Y is H, CH₃, or CH₃CH₂,

M is any mono or divalent cations, preferably H, Na, K, Ca, Mg, NH₄, andmost preferably Na.A preferred formulation to inject into the reservoir is shown below:Surfactant concentrate: 0.05 to 2.0, preferably 0.05 to 0.5. and mostpreferably 0.1 to 0.3 wt % co-surfactants/solvents: 0 to 50 wt %,preferably 0 to 25 wt %, and most preferably 5 to 25 wt %,Viscosity improving agent: 0 to 10 wt %, preferably 0 to 3 wt %, andmost preferably 0 to 0.5 wt %,Alkali: 0 to 10 wt %, preferably 0 to 5 wt %, and most preferably 0 to 2wt %, andremainder is aqueous solvent,

While the invention has been described in connection with a preferredembodiment, it is not intended to limit the scope of the invention tothe particular form set forth, but on the contrary, it is intended tocover such alternatives, modifications, and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

1. A process for the recovery of oil from subterranean reservoirs wherea surfactant composition is injected into one or more injection wellsand the oil recovered from one or more producing wells where saidsurfactant composition is comprised of a) one or more surfactants havingweak and strong anionic functionality groups, b) an aqueous basedsolvent, c) one or more co-surfactants/solvents, d) optionally aviscosity increasing agent, and e) optionally an alkali.
 2. The processfor the recovery of oil from subterranean reservoirs described in claim1 where the one or more surfactants having weak and strong anionicfunctionality groups have the weak and strong functionality groups onthe same molecule having one of the following structures:

Where m+n is 5 to 28, preferably 9 to 21 and most preferably 15 to 19, Xis 0 to 30, preferably 0 to 15, and most preferably 4 to 12, Y is H,CH₃, or CH₃CH₂, M is a mono or divalent cation, preferably H, Na, K, Ca,Mg, NH₄, and most preferably Na.
 3. The process for the recovery of oilfrom subterranean reservoirs described in claim 1 where the weak anionicfunctionality group is a carboxylate.
 4. The process for the recovery ofoil from subterranean reservoirs described in claim 1 where the stronganionic functionality group is one or more from the group sulfonate,sulfate.
 5. The process for the recovery of oil from subterraneanreservoirs described in claim 1 where the one or more surfactants havingthe weak and strong anionic functionality groups have thesefunctionalities contained on separate surfactants.
 6. The process forthe recovery of oil from subterranean reservoirs described in claim 5where the one or more surfactants having weak anionic functionality ischosen from the group carboxylated alkylphenol alkoxylates, carboxylatedlinear alcohol alkoxylates, carboxylated branched alcohol alkoxylates.7. The process for the recovery of oil from subterranean reservoirsdescribed in claim 5 where one or more surfactants having strong anionicfunctionality is chosen from the group linear alkyl aryl sulfonates,branched alkyl aryl sulfonates, aryl linear alkyl sulfonates, arylbranched alkyl sulfonates, linear alkyl ether sulfates, branched alkylether sulfates, linear alkyl ether sulfonates, branched alkyl ethersulfonates, linear alkyl sulfates, branched alkyl sulfates, linear alkylsulfonates, branched alkyl sulfonates.
 8. The process for the recoveryof oil from subterranean reservoirs described in claim 1 where the oneor more anionic surfactants is present at a concentration from about0.05, to about 2% by weight preferably from about 0.05 to about 0.5% byweight, and most preferably from about 0.1 to about 0.3% by weight. 9.The process for the recovery of oil from subterranean reservoirsdescribed in claim 1 where the co-surfactants/co-solvents is present ata concentration of 0 to about 50% by weight, preferably 0 to about 25%by weight, and most preferably from about 5 to about 25% by weight. 10.The process for the recovery of oil from subterranean reservoirsdescribed in claim 1 where the viscosity control agent is present at aconcentration from 0 and about 10% by weight, preferably from 0 to about0.3% by weight, and most preferably from 0 to about 0.5% by weight. 11.The process for the recovery of oil from subterranean reservoirsdescribed in claim 1 where the alkali is present at a concentration from0 to about 10% by weight, preferably from 0 to about 5% by weight, andmost preferably from 0 to about 2% by weight.
 12. The process for therecovery of oil from subterranean reservoirs described in claim 1 wherethe co-solvent is chosen from the group: short chain alcohol, glycol,glycerin, glycol ether.
 13. The process for the recovery of oil fromsubterranean reservoirs described in claim 1 where the alkali is chosenfrom the group: hydroxide, carbonate, silicate, borate.
 14. The processfor the recovery of oil from subterranean reservoirs described in claim1 where the aqueous solvent is chosen from the group: water, syntheticbrine, injection brine, produced brine.
 15. The process for the recoveryof oil from subterranean reservoirs described in claim 1 where the oneor more injection wells may also serve as the one or more producingwells.
 16. The process for the recovery of oil from subterraneanreservoirs described in claim 1 where the one or more injection wellsare different than the one or more producing wells.